The Fermi Paradox: A lonely galaxy?

Science is full of interesting questions and Enrico Fermi liked his questions. Whereas Frank Drake may have come up with my favourite equation, Fermi asked my favourite question – where is everybody? He was talking about aliens.

Enrico Fermi was an Italian Nobel-Prize-winning-physicist. One lunchtime in 1950 when casually discussing flying saucers with some of his physics colleagues (at the Los Alamos National Laboratory), Fermi asked, “where is everybody”? He was asking why hadn’t we been visited by intelligent alien life yet?

This might sound like an odd question, with some obvious answers, like; ‘they’re too far away’ or ‘there aren’t any’ or ‘they’re already here, haven’t you seen the crop circles, feel those 5th dimension vibrations!’ But Fermi wasn’t convinced.

Fermi enjoyed trying to find answers for seemingly impossible questions, such as how many grains of sand are there on the world’s beaches? He had talent for being able to brake such questions down into a set of assumptions and was then able to find approximate values for his assumptions based on informed reasoning (much like the Drake Equation) – see Fermi Questions.

It might sound like an odd question, and may have some seemingly obvious answers, but to Fermi, the fact that we hadn’t found proof of alien life was extremely strange.

Fermi began by reasoning that we live in moment in time and in an area of our Galaxy which aren’t particularly unusual (this is often called the Copernican Principle). So if life can arise and prosper in one area of our not-so-special Galaxy then life should be found in other similar areas of our Galaxy too. Also, our Galaxy is very old, around 13.2 billion years; life should have had time to get started in more than one place. Fermi made some quick Drake-style calculations and reasoned that given such a long amount of time, our Galaxy should be full of life.

‘So what?’ you may say, life may have emerged more than once in our Galaxy but any sci-fi geek worth their salt knows that faster than light travel is extremely unlikely (although we can still dream), and that the space between stars in our galaxy is massive, thus even if our Galaxy is teaming with life it’ll never be able to reach us. Depressing huh? We may live in a Galaxy full of aliens, but live too far away to ever meet them, this would make a particularly crap Star Trek universe.

But this might not be the case. The Milky Way (our Galaxy) is roughly 100,000 light years across. A spaceship travelling at 10% the speed of light (this is VERY fast) would take roughly 1 million years to travel from one end to the other. That’s a long journey, and a good answer to Fermi’s question, right?

Maybe not. Lots of scientists have constructed models for galactic colonization, from the simplest one above to complex percolation models which look in more detail at how long it would take for a space-faring civilization, travelling less than light-speed, to spread from planet to planet, establishing colonies which lead to future colonial expeditions to new planets. Even the longest predictions still tend to be around the hundreds of millions of years. This may sound like a long time, but if it takes 300 million years for a species to colonize the Milky Way, this would only represent 2.3% of the of the Galaxy’s age. Such a civilization could emerge halfway through the Milky Way’s existence and could travel from one end of the galaxy to the other eleven times.

So even though million-year journeys sound immensely long to humans, in terms of the age of the Milky Way, this is a heartbeat. If our Galaxy has periodically witnessed the emergence of many advanced civilizations, and there’s been ample colonization time, where is everybody? This is where the fun really starts, trying to answer Fermi’s paradox, proposing reasons why we haven’t met alien life yet?